Good explanation by Karen, and of course, previous threads will prove quite helpful.
The Borg also made appearances in Star Trek-Voyager; and it was in that series that one human girl was assimilated by the Borg when young. She was designated Seven Of Nine and later, as Karen mentioned, an attempt was made to "disassimilate" her. But that process could not be fully completed; part of her remained Borg. That seems to be the case with any who get involved in the Witness organization; it seems they cannot totally be seperated from it, their best attempts and the attempts of others notwithstanding.
I've sometimes wondered how many would just love to 'walk away' as it were, and never look back, not even needing to visit boards like this for support. I would imagine that such individuals would number very few, if any.
There was also an intriguing Voyager episode, maybe someone knows the title of it, in which some of the Borg began to experience 'independent thought' and kind of met, not bodily but in some time of place mentally, and shared some of these thoughts and actually experienced an awakening of sorts of their former selves. The Borg saw this as a tremendous threat and actually destroyed their own members to keep such a contagion from spreading. Anyone recall that episode? It certainly bears similarity to what many have experienced with the JW faith.